1. Field of the Invention
The present invention relates to a method and system for measuring a urinary flow rate, and more particularly to a method and system for measuring a urinary flow rate, in which impact noise caused by urine is minimized to measure the urinary flow rate using a plurality of load cells.
2. Description of the Prior Art
Men discharge urine through the urethra encircled by the prostate gland located under the bladder. In detail, the prostate gland is found only in the male, and refers to a glandular reproductive organ that has chestnut-shaped soft tissue under the bladder with weight of about 20 g and encircles the urethra. The prostate gland is hypertrophied by, for instance, prostatitis, which is called prostatic hypertrophy. This disease is one of the representative chronic diseases of an aged society with which about 50% to 80% of adult men, particularly men in the fifties or more, are attacked. When this prostatic hypertrophy occurs, the urethra encircled by the prostate gland is compressed to cause abnormal urination as well as sexual dysfunction.
A method of determining whether or not the prostate gland is abnormal; namely whether or not prostatic hypertrophy exists, as described above, by employing uroflowmetry that continuously measures a urinary flow rate signal indicating an amount of urine per unit time during urination. This method is an indispensable biomedical test in the event of diagnosis of the prostatic hypertrophy.
The conventional uroflowmetry is typically based on measurement of the weight of urine. As schematically illustrated in FIG. 1, urine 13 is collected into a container 10 having a predetermined diameter, and a load cell device, i.e. a weight sensor, which is mounted under the container 10 and measures a weight of urine, is situated. A change in the weight (mass) of urine is measured during urination. This method is based on the principle that the weight W measured by the weight sensor 12 is proportional to a volume V of urine collected into the container 10. For example, assuming that the weight of urine represented by the weight sensor 12 be W, that the volume of urine collected into the container 10 be V, that a cross section of the container be A, that a density of urine be ρ, and that a height of urine collected into the container 10 be h, the weight W is expressed by the following equation.W=ρgAh.
Here, the product of the cross section A of the container and the height h of urine equal to the volume V of urine, the equation is as follows.W=ρgAh=ρgV
Here, the density ρ of urine is nearly equal to water, and thus is regarded as 1, and g is the gravitational constant. The equivalent equation can be expressed as follows.W=ρgAh=ρgV∝V
Accordingly, the change in the volume of urine can be found by measuring the change in the weight of urine collected during urination. However, a biological variable that is to be actually calculated in order to determine whether or not the prostate gland is abnormal is a urinary flow rate signal, and thus a method of calculating the change in the volume of urine into the urinary flow rate signal is used. In other words, since the urinary flow rate is defined as a rate of change in volume over time, a weight signal proportional to the volume is differentiated with respect to time, and thereby the urinary flow rate is yielded.
An example of carrying out the uroflowmetry using the conventional method is shown in the graph of FIG. 2.
In detail, FIG. 2 shows the results of the conventional uroflowmetry along with a volume signal obtained by measuring the weight of urine of a normal person, a urinary flow rate signal differentiating the volume signal, and various diagnosis parameters obtained by analysis. (Textbook of Voiding Dysfunction and Female Urology, Korean Continence Society, Il-Jo-Gak, 331 p, 2003).
In the conventional method and apparatus for the uroflowmetry as described above, the urinary flow rate is tested by continuously measuring a change in weight of urine using the weight sensor during collecting the urine into the container, and analyzing the volume signal based on the measurement, the urinary flow rate signal differentiating the volume signal, and so on.
However, in the conventional method and apparatus, when the urine 13 is collected into the container 10 during urination, a stream of urine (dotted line of FIG. 1) directly touches the bottom of the container 10, and thus the bottom of the container 10 gets an additional impact due to momentum (mass×velocity) of the stream of urine in addition to the weight of urine. Thus, in addition to the weight of urine, impulse of urine is transmitted to the weight sensor 12. An effect of the impact is randomly transmitted to the weight sensor 12 according to amount and velocity of the stream of urine, and thus acts as measurement noise. Further, since the urine is not contracted or expanded like gas, there is no damping action. As such, after the urine is collected at a predetermined amount, the impulse applied to a surface of the urine is transmitted intact to the weight sensor 12 under the bottom of the container 10. This leads to a decrease in reliability when the differentiation and the diagnosis parameters for obtaining the urinary flow rate are calculated.
FIG. 3 is a graph showing the results of test measurement based on a conventional method for uroflowmetry, in which the test is done by pouring water of 800 ml instead of the urine like urination, and measuring a weight of water to obtain a volume signal. It can be found that the measurement noise exists throughout the volume signal. In order to prevent this impact effect, the water is adapted to flow down along a wall of the container, thereby minimizing the impulse. To this end, a separate funnel is typically used. Thus, the separate funnel must be precisely designed and manufactured so as to be fitted to the collecting container, and then be inserted into the collecting container, which is troublesome.